It is well-known that during the cleaning of medical instruments or of parts of food-treating machines or of parts of pharmaceutical installations it is highly mandatory that the cleaning action be as effective and complete as possible. For, it must be ensured under any circumstances that during the subsequent use of such objects a transfer of pathogenic agents, organisms, germs or viruses is absolutely excluded.
In the clinical area the protection against pathogenic agents or organisms is not achieved through the cleaning before the application of such instruments but instead through sterilization following the cleaning process. The object of the cleaning is to reduce the initial contamination of the instruments to be sterilized in order to increase the sterilization performance, the so-called sterilization probability. A further object of the cleaning process is to remove unwanted substances, i.e. to remove soiling in order to optimize the access of the sterilizing agents to those surfaces of the instruments that shall be treated.
Insofar, substantial problems arise in connection with the cleaning of so-called hollow shaft instruments as are used in the minimum invasive or endoscopic surgery. Such instruments are provided with an elongate tubular shaft. The tubular shaft has an operating element on its front terminal end, for example a medical forceps, whereas the rearward terminal end is provided with corresponding actuators, for example actuating levers. In order to interconnect the operating elements with the corresponding actuators, an appropriate rod or a Bowden pull wire is arranged within the hollow shaft.
During the application of such medical instruments the hollow shaft is, for example, pushed through the abdominal wall of a patient so that a surgical operation may be carried out on an inner organ of the patient by means of the operating elements. The operating elements as well as the lower portion of the hollow shaft will come in contact with blood or other body liquids. Due to a capillary action within the hollow shaft, these liquids will rise upwardly within the hollow shaft.
After the operation is finished, the instruments are normally not immediately cleaned because in ordinary hospitals the cleaning installations are normally located distant from the operating catheters. Due to the time lapsing accordingly, the liquid will partially dry on the instrument. The subsequent cleaning of the instrument may then be difficult for various reasons. First, the liquid may have penetrated into cavities, annular grooves and the like which are hardly accessible. Further, the liquid may have partially dried up for the reasons mentioned before so that the cleaning is also much for difficult for these reasons.
On the other hand side, instruments of the afore-mentioned kind are relatively expensive. Therefore, they have to be re-used as many times as possible. The same holds true for other invasive instruments, for example for rigid or flexible endoscopes. The same applies for other types of instruments which in spite of their relatively high price are until today used as disposables, for example catheters.
Similar problems arise in other areas, for example in the food industry or in the pharmaceutical industry where care must be taken that the parts of the machines treating food or pharmaceutical products have to be diligently cleaned after each working cycle.
For the reasons explained above, it is well-known that cleaning aspects have to be taken into account already during the design of the corresponding object, for example during the design of a medical instrument for endoscopic surgery. It is, therefore, well-known to optimize the design of such instruments under the aspect of cleanability. It is, for example, known to provide instruments of this kind with particular features, for example with rinsing channels or the like to facilitate cleaning after the use of such instruments.
On the other hand side, there is a need in the field of cleaning installations (washing machines) and of cleaning agents, respectively, for such objects, instruments etc. to continuously improve such products so that the difficult cleaning problems mentioned above and other comparable cleaning problems may be solved.
In view of this background there is a need to have a method enabling to determine the cleaning action under objective standards and reproducibly. If such a method were at hand, it would be possible to continuously refine the design of such objects and instruments by continuously applying the method. The same would apply for the design of cleaning installations and washing machines and also for the creation of cleaning agents because the cleaning action of such installations or agents could also be controlled with a reproducible method mentioned above. For optimizing the design of objects and instruments under cleanability aspects, the method would have to be applied on differently designed objects and instruments while using the same cleaning method, the same cleaning instruments and the same cleaning action for obtaining reproducible results during the evolution, i.e. optimization of the instrument or object design. In the case of the optimizing of cleaning installations, washing machines or cleaning agents, the method would have to be used on the same reference instruments or reference objects for varifying the cleaning action on a neutral and reproducible basis.
A method for validating and controlling the cleaning of hollow shaft instruments is disclosed in German journal "Zentral Sterilisation", 2 (1994), pp. 313-324.
According to this prior art method hollow shaft instruments are soiled with radioactively marked blood. The distribution of the test contamination so generated is topographically determined before and after the cleaning. For that purpose an experimental set up is used in used in which hollow shaft instruments are soiled with blood, where the blood had been provided with radioactive 99.sup.th technetium. For that purpose makroalbumines are first provided with the radioactive technetium. The radioactive makroalbumines are then mixed with fresh, i.e. coagulable blood. By means of a .gamma.-camera the soiled hollow shaft instruments are measured, are then rinsed and are finally measured a second time. The measurements are made by detecting the counts per second. The cleaning action is then determined through the ratio of the measured values before and after the cleaning. The natural half lifetime of technetium (approximately six hours) is taken into account.
This prior art method yields only relative results but no absolute results in view of the actual amount or mass of the remaining soiling. It is impossible to directly convert the measured counts per time into mass units because the behaviour of radioactively marked makroalbumines is not known in detail, in particular not in connection with the metallic environment. Further, the dissociative behavior of technetium in this regard is not known in detail. Due to these reasons the measurement may be faulty when in spite of the presence of a relatively large mass or residual soiling, only relatively small radiation (counts per time) is measured.
It is, therefore, an object underlying the invention to improve the methods of the kind as specified at the outset such that reproducible results are obtained, allowing in particular to actually determine the existing mass of residual soiling or any soiling quantitatively and, moreover, independent of the prevailing initial radiation at the moment when the inventive method is initiated.
According to a first group of inventive method in which the cleaning action on a cleaned object is determined, this object is met by the following method steps:
a) providing a predetermined soiling substance; PA1 b) adding to said soiling substance a radioactive marker having a half life period T, said soiling substance provided with said radioactive marker having together a first mass m.sub.0 and a radiation; PA1 c) measuring said first mass m.sub.0 ; PA1 d) simultaneously with said measuring of said first mass m.sub.0 measuring a first intensity I.sub.0 of said radiation and starting a measurement of time t; PA1 e) at least partially inserting said object into said soiling substance provided with said radioactive marker such that a second mass m.sub.1 of said soiling substance provided with said radioactive marker is introduced into at least a portion of said object, thereby contaminating said object; PA1 f) cleaning said object; PA1 g) measuring a third intensity I.sub.2 of said radiation at a moment in time t.sub.2 ; PA1 h) determining a third mass m.sub.2 of a soiling having remained on said object after said step of cleaning according to the formula: ##EQU1## where r.sub.(t, . . . ) is a predetermined proportionality function for taking into account the dissociative behaviour of bonding between the radioactive marker and the object as a carrier. PA1 a) providing a predetermined soiling substance; PA1 b) adding to said soiling substance a radioactive marker having a half life period T, said soiling substance provided with said radioactive marker having together a first mass m.sub.0 and a radiation; PA1 c) measuring said first mass m.sub.0 ; PA1 d) simultaneously with said measuring of said first mass m.sub.0 measuring a first intensity I.sub.0 of said radiation and starting a measurement of time t; PA1 e) at least partially inserting said object into said soiling substance provided with said radioactive marker such that a second mass m.sub.1 of said soiling substance provided with said radioactive marker is introduced into at least a portion of said object thereby contaminating said object, said second mass m.sub.1 having a radiation of a second intensity I.sub.1 ; PA1 f) measuring said second intensity I.sub.1 of said second mass m.sub.1 on said contaminated object at a moment in time t.sub.1 ; and PA1 g) determining said second mass m.sub.1 according to the formula: ##EQU2## where r.sub.(t, . . . ) is a predetermined proportionality function for taking into account the dissociative behaviour of bonding between the radioactive marker and the object as a carrier.
According to a second group of inventive methods in which the amount of soiling on objects is determined, the above-mentioned object is met by the following method steps:
The object underlying the invention thus entirely solved. According to the afore-mentioned first group of inventive methods one determines the mass (m.sub.2) having remained on the object after cleaning. Correspondingly, in the second group of inventive methods one determines the mass (m.sub.1) being on the object before it undergoes a cleaning action.
In both cases it is possible to obtain an absolute mass value. This value may be determined with any conceivable kind of radiation that makes sense for this particular purpose.
According to a preferred embodiment of the invention, the two groups of methods are combined with each other by determining the ration of the two masses. In such a way it is possible to obtain an exact parameter for the cleaning action. This parameter may be used a basis for the design of the object or for the kind of the cleaning process or for the cleaning agent where one of these two is held constant to optimize the other.
According to another preferred embodiment of the invention, at least one of the intensities (I.sub.1, I.sub.2) of the radiation of the second mass (m.sub.1) or the third mass (m.sub.2), respectively, is localizedly measured on the object.
By this measure, known per se, one can detect the cleaning action selectively on particularly critical areas, for example on narrow areas of joints or the like.
For that purpose it is preferred that at least one of the intensities (I.sub.1, I.sub.2) of the radiation of the second mass (m.sub.1) and the third mass (m.sub.3), respectively is measured by a camera sensitive for radioactive radiation, in particular for .gamma.-radiation, as also known per se.
It was already mentioned that the inventive method may be used for various applications. A preferred field of application is the field of medical instruments, in particular of hollow shaft instruments for minimum invasive or endoscopic surgery.
Another important medical field of application is the cleaning of flexible endoscopes and the reprocessing of intravasal catheters, in particular coronary catheters. In view of the urgent need within public health care to reduce costs, the validation of processes for reprocessing catheters in lieu of using disposables, will become much more important in the future.
Apart from these applications numerous other applications are possible, for example with respect to parts of food-processing machines or of pharmaceutical installations.
The inventive method and applications preferably relate to situations where the objects to be cleaned shall be cleaned by a machine. However, the invention is not limited to this application, instead, the invention may also be used in cases where the objects are cleaned by hand.
Further, it was already pointed out that the inventive method may also be used for various other purposes, namely for optimizing the design-based cleanability of medical instruments but also for optimizing the design-based cleaning action of washing machines for objects of the kind of interest and also for optimizing the development of cleaning agents.